Light emitting devices

ABSTRACT

Light-emitting devices, and related components, systems and methods are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §119 to thefollowing U.S. Provisional Patent Applications: 60/462,889, filed Apr.15, 2003; 60/474,199, filed May 29, 2003; 60/475,682, filed Jun. 4,2003; 60/503,653, filed Sep. 17, 2003; 60/503,654 filed Sep. 17, 2003;60/503,661, filed Sep. 17, 2003; 60/503,671, filed Sep. 17, 2003;60/503,672, filed Sep. 17, 2003; 60/513,807, filed Oct. 23, 2003; and60/514,764, filed Oct. 27, 2003. Each of these applications isincorporated herein by reference.

TECHNICAL FIELD

[0002] The invention relates to light-emitting devices, and relatedcomponents, systems and methods.

BACKGROUND

[0003] A light emitting diode (LED) often can provide light in a moreefficient manner than an incandescent light source and/or a fluorescentlight source. The relatively high power efficiency associated with LEDshas created an interest in using LEDs to displace conventional lightsources in a variety of lighting applications. For example, in someinstances LEDs are being used as traffic lights and to illuminate cellphone keypads and displays.

[0004] Typically, an LED is formed of multiple layers, with at leastsome of the layers being formed of different materials. In general, thematerials and thicknesses selected for the layers determine thewavelength(s) of light emitted by the LED. In addition, the chemicalcomposition of the layers can be selected to try to isolate injectedelectrical charge carriers into regions (commonly referred to as quantumwells) for relatively efficient conversion to optical power. Generally,the layers on one side of the junction where a quantum well is grown aredoped with donor atoms that result in high electron concentration (suchlayers are commonly referred to as n-type layers), and the layers on theopposite side are doped with acceptor atoms that result in a relativelyhigh hole concentration (such layers are commonly referred to as p-typelayers).

[0005] A common approach to preparing an LED is as follows. The layersof material are prepared in the form of a wafer. Typically, the layersare formed using an epitaxial deposition technique, such asmetal-organic chemical vapor deposition (MOCVD), with the initiallydeposited layer being formed on a growth substrate. The layers are thenexposed to various etching and metallization techniques to form contactsfor electrical current injection, and the wafer is subsequentlysectioned into individual LED chips. Usually, the LED chips arepackaged.

[0006] During use, electrical energy is usually injected into an LED andthen converted into electromagnetic radiation (light), some of which isextracted from the LED.

SUMMARY

[0007] The invention relates to light-emitting devices, and relatedcomponents, systems and methods.

[0008] In one embodiment, the invention features a light-emitting devicethat includes a multi-layer stack of materials. The multi-layer stack ofmaterials includes a light-generating region and a first layer supportedby the light-generating region. The surface of the first layer isconfigured so that light generated by the light-generating region canemerge from the light-emitting device via the surface of the firstlayer. The surface of the first layer has a dielectric function thatvaries spatially according to a pattern, and the pattern has an ideallattice constant and a detuning parameter with a value greater thanzero.

[0009] In another embodiment, the invention features a light-emittingdevice that includes a multi-layer stack of materials. The multi-layerstack of materials includes a light-generating region and a first layersupported by the light-generating region. The surface of the first layeris configured so that light generated by the light-generating region canemerge from the light-emitting device via the surface of the firstlayer, and the surface has a dielectric function that varies spatiallyaccording to a nonperiodic pattern.

[0010] In a further embodiment, the invention features a light-emittingdevice that includes a multi-layer stack of materials. The multi-layerstack of materials includes a light-generating region and a first layersupported by the light-generating region. The surface of the first layeris configured so that light generated by the light-generating region canemerge from the light-emitting device via the surface of the firstlayer, and the surface has a dielectric function that varies spatiallyaccording to a complex periodic pattern.

[0011] In one embodiment, the invention features a light-emitting devicethat includes a multi-layer stack of materials. The multi-layer stack ofmaterials includes a layer of n-doped material, a layer of p-dopedmaterial, and a light-generating region. The light-emitting device alsoincludes a layer of reflective material that is capable of reflecting atleast about 50% of light generated by the light-generating region thatimpinges on the layer of reflective material. The surface of the layerof n-doped material is configured so that light generated by thelight-generating region can emerge from the light-emitting device viathe surface of the layer of n-doped material. The surface of the layerof n-doped material has a dielectric function that varies spatiallyaccording to a pattern, and the distance between the layer of p-dopedmaterial and the layer of reflective material is less than the distancebetween the layer of n-doped material and the layer of reflectivematerial.

[0012] In another embodiment, the invention features a light-emittingdevice that includes a multi-layer stack of materials including alight-generating region and a first layer supported by thelight-generating region. The surface of the first layer is configured sothat light generated by the light-generating region can emerge from thelight-emitting device via the surface of the first layer, and thesurface of the first layer has a dielectric function that variesspatially according to a pattern. The light-emitting device alsoincludes a layer of reflective material that is capable of reflecting atleast about 50% of light generated by the light-generating region thatimpinges on the layer of reflective material. The light-generatingregion is between the layer of reflective material and the first layer,and the pattern does not extend beyond the first layer.

[0013] In a further embodiment, the invention features a light-emittingdevice that includes a multi-layer stack of materials. The multi-layerstack of materials includes a light-generating region, and a first layersupported by the light-generating region. The surface of the first layeris configured so that light generated by the light-generating region canemerge from the light-emitting device via the surface of the firstlayer. The light-emitting device also includes a material in contactwith the surface of the first layer, where the material has an index ofrefraction less than about 1.5. The light emitting device is packaged.

[0014] In one embodiment, the invention features a light-emitting devicethat includes a multi-layer stack of materials. The multi-layer stack ofmaterials includes a light-generating region and a first layer supportedby the light-generating region. The surface of the first layer isconfigured so that light generated by the light-generating region canemerge from the light-emitting device via the surface of the firstlayer. The surface of the first layer has a dielectric function thatvaries spatially according to a pattern. The light-emitting device alsoincludes a phosphor material supported by the surface of the firstlayer. The sidewalls of the light-emitting device are substantiallydevoid of the phosphor material.

[0015] In another embodiment, the invention features a method of makinga wafer. The method includes disposing a phosphor material on a surfaceof the wafer. The wafer includes a plurality of light-emitting devices.Each light-emitting device includes a multi-layer stack of materialsincluding a light-generating region and a first layer supported by thelight-generating region. The surface of the first layer is configured sothat light generated by the light-generating region can emerge from thelight-emitting device via the surface of the first layer, and thesurface of the first layer has a dielectric function that variesspatially according to a pattern.

[0016] In a further embodiment, the invention features a light-emittingdevice that includes a multi-layer stack of materials. The multi-layerstack of materials includes a light-generating region and a first layersupported by the light-generating region. The surface of the first layeris configured so that light generated by the light-generating region canemerge from the light-emitting device via the surface of the firstlayer, and the surface of the first layer has a dielectric function thatvaries spatially according to a pattern. The light-emitting device alsoincludes a phosphor material configured so that light generated by thelight-generating region that emerges via the surface of the first layerinteracts with the phosphor material so that light that emerges from thephosphor layer is substantially white light. The ratio of the height ofthe light-emitting device to an area of the light-emitting device issufficiently small enough for the white light to extend in alldirections.

[0017] In one embodiment, the invention features a light-emitting devicethat includes a multi-layer stack of materials. The multi-layer stack ofmaterials includes a light-generating region, and a first layersupported by the light-generating region. The surface of the first layeris configured so that light generated by the light-generating region canemerge from the light-emitting device via the surface of the firstlayer. The light-emitting device also includes a first sheet formed of amaterial that is substantially transparent to light that emerges fromthe light-emitting device, and a second sheet that includes a phosphormaterial. The second sheet is adjacent the first sheet. Thelight-emitting device is packaged, and the first and second sheets forma portion of the package for the light-emitting device.

[0018] In another embodiment, the invention features a light-emittingdevice that includes a multi-layer stack of materials including alight-generating region and a first layer supported by thelight-generating region. The surface of the first layer is configured sothat light generated by the light-generating region can emerge from thelight-emitting device via the surface of the first layer. The surface ofthe first layer has a dielectric function that varies spatiallyaccording to a pattern, and the pattern is configured so that lightgenerated by the light-generating region that emerges from thelight-emitting device via the surface of the first layer is morecollimated than a lambertian distribution of light.

[0019] In a further embodiment, the invention features a wafer thatincludes a plurality of light-emitting devices. At least some of thelight-emitting devices include a multi-layer stack of materials. Themulti-layer stack of materials includes a light-generating region and afirst layer supported by the light-generating region. The surface of thefirst layer is configured so that light generated by thelight-generating region can emerge from the light-emitting device viathe surface of the first layer. The surface of the first layer has adielectric function that varies spatially according to a pattern, andthe pattern is configured so that light generated by thelight-generating region that emerges from the light-emitting device viathe surface of the first layer is more collimated than a lambertiandistribution of light. The wafer has at least about five (e.g., at leastabout 25, at least about 50) light-emitting devices per squarecentimeter.

[0020] In one embodiment, the invention features a light-emitting devicethat includes a multi-layer stack of materials. The multi-layer stack ofmaterials includes a light-generating region and a first layer supportedby the light-generating region so that, during use of the light-emittingdevice, light generated by the light-generating region can emerge fromthe light-emitting device via a surface of the first layer. The surfaceof the first layer has a dielectric function that varies spatiallyaccording to a pattern, and at least about 45% (e.g., at least about50%, at least about 60%, at least about 70%) of the total amount oflight generated by the light-generating region that emerges from thelight-emitting device emerges via the surface of the light-emittingdevice.

[0021] In another embodiment, the invention features a light-emittingdevice that includes a multi-layer stack of materials. The multi-layerstack of materials includes a light-generating region and a first layersupported by the light-generating region so that, during use of thelight-emitting device, light generated by the light-generating regioncan emerge from the light-emitting device via a surface of the firstlayer. The light-emitting device has an edge which is at least about onemillimeter (e.g., at least about 1.5 millimeters, at least about towmillimeters, at least about 2.5 millimeters) long, and thelight-emitting device is designed so that the extraction efficiency ofthe light-emitting device is substantially independent of the length ofthe edge of the length of the edge.

[0022] In a further embodiment, the invention features a light-emittingdevice that includes a multi-layer stack of materials. The multi-layerstack of materials includes a light-generating region and a first layersupported by the light-generating region so that, during use of thelight-emitting device, light generated by the light-generating regioncan emerge from the light-emitting device via a surface of the firstlayer. The light-emitting device has an edge which is at least about onemillimeter (e.g., at least about 1.5 millimeters, at least about towmillimeters, at least about 2.5 millimeters) long, and thelight-emitting device is designed so that the quantum efficiency of thelight-emitting device is substantially independent of the length of theedge of the length of the edge.

[0023] In one embodiment, the invention features a light-emitting devicethat includes a multi-layer stack of materials. The multi-layer stack ofmaterials includes a light-generating region and a first layer supportedby the light-generating region so that, during use of the light-emittingdevice, light generated by the light-generating region can emerge fromthe light-emitting device via a surface of the first layer. Thelight-emitting device has an edge which is at least about one millimeter(e.g., at least about 1.5 millimeters, at least about tow millimeters,at least about 2.5 millimeters) long, and the light-emitting device isdesigned so that the wall plug efficiency of the light-emitting deviceis substantially independent of the length of the edge of the length ofthe edge.

[0024] In another embodiment, the invention features a method of makinga light-emitting device. The method includes bonding a layer of areflective material with a layer of p-doped material. The light-emittingdevice includes a multi-layer stack of materials including the layer ofp-doped material, a light-generating region, and a first layer. Thefirst layer includes a surface having a dielectric function that variesspatially according to a pattern, and the reflective material is capableof reflecting at least about 50% of light generated by thelight-generating region that impinges on the layer of reflectivematerial.

[0025] In a further embodiment, the invention features a method ofmaking a light-emitting device. The method includes disbonding asubstrate bonded with a first layer. The first layer forms a portion ofa multi-layer stack of materials that includes a light-generatingregion, and the method forms a light-emitting device in which a surfaceof the first layer has a surface with a dielectric function that variesspatially according to a pattern.

[0026] Embodiments can feature one or more of the following aspects.

[0027] The multi-layer stack of materials can be formed of a multi-layerstack of semiconductor materials. The first layer can be a layer ofn-doped semiconductor material, and the multi-layer stack can furtherinclude a layer of p-doped semiconductor material. The light-generatingregion can be between the layer of n-doped semiconductor material andthe layer of p-doped semiconductor material.

[0028] The light-emitting device can further include a support thatsupports the multi-layer stack of materials.

[0029] The light-emitting device can further include a layer ofreflective material that is capable of reflecting at least about 50% oflight generated by the light-generating region that impinges on thelayer of reflective material. The layer of reflective material can bebetween the support and the multi-layer stack of materials. The distancebetween the layer of p-doped semiconductor material and the layer ofreflective material can be less than a distance between the layer ofn-doped semiconductor material and the layer of reflective material. Thelight-emitting device can further include a p-ohmic contact layerbetween the layer of p-doped material and the layer of reflectivematerial.

[0030] The light-emitting device can further include a current-spreadinglayer between the first layer and the light-generating region.

[0031] The multi-layer stack of materials can be formed of semiconductormaterials, such as, for example, III-V semiconductor materials, organicsemiconductor materials and/or silicon.

[0032] In some embodiments, the pattern does not extend into thelight-generating region.

[0033] In certain embodiments, the pattern does not extend beyond thefirst layer.

[0034] In some embodiments, the pattern extends beyond the first layer.

[0035] The light-emitting device can further include electrical contactsconfigured to inject current into the light-emitting device. Theelectrical contacts can be configured to vertically inject electricalcurrent into the light-emitting device.

[0036] The pattern can be partially formed of a component selected from,for example, holes in the surface of the first layer, pillars in thefirst layer, continuous veins in the first layer, discontinuous veins inthe first layer and combinations thereof.

[0037] In some embodiments, the pattern can be selected from triangularpatterns, square patterns, and grating patterns.

[0038] In certain embodiments, the pattern can be selected fromaperiodic patterns, quasicrystalline patterns, Robinson patterns, andAmman patterns. In some embodiments, the pattern is a Penrose pattern.

[0039] In some embodiments, the pattern is selected from honeycombpatterns and Archimidean patterns. In certain embodiments, a pattern(e.g., a honeycomb pattern) can have holes with different diameters.

[0040] The pattern can be partially formed of holes in the surface ofthe first layer.

[0041] The detuning parameter can be, for example, at least about 1% ofthe ideal lattice constant and/or at most about 25% of the ideal latticeconstant. In some embodiments, the pattern can correspond to asubstantially randomly detuned ideal pattern.

[0042] The pattern can be configured so that light emitted by thesurface of the first layer has a spectrum of radiation modes, and thespectrum of radiation modes is substantially the same as acharacteristic emission spectrum of the light-generating region.

[0043] The light-emitting device can be, for example, a light-emittingdiode, a laser, or an optical amplifier. Examples of light-emittingdevices include organic light-emitting devices (OLEDs), flatsurface-emitting LEDs, and high brightness light-emitting devices(HBLEDs).

[0044] In some embodiments, the surface of the first layer has featureswith a size of less than about λ/5, where λ is a wavelength of lightthat can be emitted by the first layer.

[0045] In certain embodiments, the light-emitting device is packaged(e.g., in the form of a packaged die). In some embodiments, a packagedlight-emitting device can be free of an encapsulant material.

[0046] In some embodiments, the material in contact with the surface ofthe first layer is a gas (e.g., air). The gas can have a pressure ofless than about 100 Torr.

[0047] In certain embodiments, the material in contact with the surfaceof the first layer has an index of refraction of at least about one.

[0048] In some embodiments, a packaged LED includes a cover. The covercan include a phosphor material. The cover can be configured so thatlight generated by the light-generating region that emerges via thesurface of the first layer can interact with the phosphor material, andso that light that emerges via the surface of the first layer andinteracts with the phosphor material emerges from the cover assubstantially white light.

[0049] In certain embodiments, the light-emitting device furtherincludes a first sheet comprising a material that is substantiallytransparent to light that emerges from the light-emitting device, and asecond sheet that includes a phosphor material. The second sheet can beadjacent the first sheet, and a material having an index of refractionof less than about 1.5 can be between the first sheet and the surface ofthe first layer. The first and second sheets can be configured so thatlight generated by the light-generating region that emerges via thesurface of the first layer can interact with the phosphor material, andso that light that emerges via the surface of the first layer andinteracts with the phosphor material emerges from the second sheet assubstantially white light.

[0050] The phosphor material can be disposed on the surface of the firstlayer.

[0051] Methods of making a wafer can include disposing the phosphormaterial to form of a layer having a thickness that varies by less thanabout 20%. The methods can include flattening the layer of the phosphormaterial so that a thickness of the layer of the phosphor materialvaries by less than about 20%. The methods can also include flatteningthe phosphor material after disposing the phosphor material on thesurface of the first layer. The phosphor material can be, for example,spin-coated on the surface of the wafer. The methods can include forminga plurality of the light emitting devices from the wafer, and separatingat least some of the light-emitting devices from each other.

[0052] In some embodiments, when light generated by the light-generatingregion emerges from the light-emitting device via the surface of thefirst layer, at least about 40% of the light emerging via the surface ofthe first layer emerges within at most about 30° of an angle normal tothe surface of the first layer.

[0053] In certain embodiments, the filling factor of the light-emittingdevice is at least about 10% and/or at most about 75%.

[0054] Methods of making a light-emitting device can further include,before bonding the layer of the reflective material with the layer ofp-doped material, bonding the first layer with a substrate, themulti-layer stack of materials being between the substrate and the layerof reflective material. The methods can also include forming a bondinglayer between the first layer and the substrate. The methods can alsoinclude removing the substrate. The methods can further include lappingand polishing steps after removing the substrate. The substrate can beremoved after bonding the layer of the reflective material with thefirst layer. Removing the substrate can include heating a bonding layerdisposed between the first layer and the substrate. Heating the bondinglayer can decompose at least a portion of the bonding layer. Heating thebonding layer can include exposing the bonding layer to radiationemitted by a laser. Removing the substrate can include exposing thesubstrate using a laser liftoff process. Removing the substrate canresult in the surface of the first layer becoming substantially flat.The methods can further include, before forming the pattern in thesurface of the first layer, planarizing the surface of the first layerafter the first substrate is removed. Planarizing the surface of thefirst layer can include chemical-mechanical polishing the surface of thefirst layer. Planarizing the surface of the first layer can reduce theroughness of the surface of the first layer to greater than about λ/5,where λ is a wavelength of light that can be emitted by the first layer.Forming the pattern can include using nanolithography. The methods canalso include disposing a substrate on the layer of reflective material.The methods can further include disposing a current-spreading layerbetween the first layer and the light-generating region.

[0055] Embodiments can feature one or more of the following advantages.

[0056] In certain embodiments, an LED and/or a relatively large LED chipcan exhibit relatively high light extraction.

[0057] In some embodiments, an LED and/or a relatively large LED chipcan exhibit relatively high surface brightness, relatively high averagesurface brightness, relatively low need for heat dissipation orrelatively high rate of heat dissipation, relatively low etendue and/orrelatively high power efficiency.

[0058] In certain embodiments, an LED and/or a relatively large LED chipcan be designed so that relatively little light emitted by the LED/LEDchip is absorbed by packaging.

[0059] In some embodiments, a packaged LED (e.g., a relatively largepackaged LED) can be prepared without using an encapsulant material.This can result in a packaged LED that avoids certain problemsassociated with the use of certain encapsulant materials, such asreduced performance and/or inconsistent performance as a function oftime, thereby providing a packaged LED that can exhibit relatively goodand/or reliable performance over a relatively long period of time.

[0060] In certain embodiments, an LED (e.g., a packaged LED, which canbe a relatively large packaged LED) can include a relatively uniformcoating of a phosphor material.

[0061] In some embodiments, an LED (e.g., a packaged LED, which can be arelatively large packaged LED) can be designed to provide a desiredlight output within a particular angular range (e.g., within aparticular angular range relative to the LED surface normal).

[0062] In some embodiments, an LED and/or a relatively large LED chipcan be prepared by a process that is relatively inexpensive.

[0063] In certain embodiments, an LED and/or a relatively large LED chipcan be prepared by a process that can be conducted on a commercial scalewithout incurring costs that render the process economically unfeasible.

[0064] Features and advantages of the invention are in the description,drawings and claims.

DESCRIPTION OF DRAWINGS

[0065]FIG. 1 is a side view of an LED with a patterned surface.

[0066]FIG. 2 is a top view the patterned surface of the LED of FIG. 1.

[0067]FIG. 3 is a graph of an extraction efficiency of an LED with apatterned surface as function of a detuning parameter.

[0068]FIG. 4 is a schematic representation of the Fourier transformationof a patterned surface of an LED.

[0069]FIG. 5 is a graph of an extraction efficiency of an LED with apatterned surface as function of nearest neighbor distance.

[0070]FIG. 6 is a graph of an extraction efficiency of an LED with apatterned surface as function of a filling factor.

[0071]FIG. 7 is a top view a patterned surface of an LED.

[0072]FIG. 8 is a graph of an extraction efficiency of LEDs withdifferent surface patterns.

[0073]FIG. 9 is a graph of an extraction efficiency of LEDs withdifferent surface patterns.

[0074]FIG. 10 is a graph of an extraction efficiency of LEDs withdifferent surface patterns.

[0075]FIG. 11 is a graph of an extraction efficiency of LEDs withdifferent surface patterns.

[0076]FIG. 12 is a schematic representation of the Fouriertransformation two LEDs having different patterned surfaces comparedwith the radiation emission spectrum of the LEDs.

[0077]FIG. 13 is a graph of an extraction efficiency of LEDs havingdifferent surface patterns as a function of angle.

[0078]FIG. 14 is a side view of an LED with a patterned surface and aphosphor layer on the patterned surface.

[0079]FIG. 15 is a side view of a epitaxial layer precursor to an LEDwith a patterned surface.

[0080]FIG. 16 is a side view of a epitaxial layer precursor to an LEDwith a patterned surface.

[0081]FIG. 17 is a side view of a epitaxial layer precursor to an LEDwith a patterned surface.

[0082]FIG. 18 is a side view of a epitaxial layer precursor to an LEDwith a patterned surface.

[0083]FIG. 19 is a side view of a epitaxial layer precursor to an LEDwith a patterned surface.

[0084] Like reference symbols in the various drawings indicate likeelements.

DETAILED DESCRIPTION

[0085]FIG. 1 shows a side view of an LED 100 in the form of a packageddie. LED 100 includes a multi-layer stack 122 disposed on a submount120. Multi-layer stack 122 includes a 320 nm thick silicon doped(n-doped) GaN layer 134 having a pattern of openings 150 in its uppersurface 110. Multi-layer stack 122 also includes a bonding layer 124, a100 nm thick silver layer 126, a 40 nm thick magnesium doped (p-doped)GaN layer 128, a 120 nm thick light-generating region 130 formed ofmultiple InGaN/GaN quantum wells, and a AlGaN layer 132. An n-sidecontact pad 136 is disposed on layer 134, and a p-side contact pad 138is disposed on layer 126. An encapsulant material (epoxy having an indexof refraction of 1.5) 144 is present between layer 134 and a cover slip140 and supports 142. Layer 144 does not extend into openings 150.

[0086] Light is generated by LED 100 as follows. P-side contact pad 138is held at a positive potential relative to n-side contact pad 136,which causes electrical current to be injected into LED 100. As theelectrical current passes through light-generating region 130, electronsfrom n-doped layer 134 combine in region 130 with holes from p-dopedlayer 128, which causes region 130 to generate light. Light-generatingregion 130 contains a multitude of point dipole radiation sources thatemit light (e.g., isotropically) within the region 130 with a spectrumof wavelengths characteristic of the material from whichlight-generating region 130 is formed. For InGaN/GaN quantum wells, thespectrum of wavelengths of light generated by region 130 can have a peakwavelength of about 445 nanometers (nm) and a full width at half maximum(FWHM) of about 30 nm.

[0087] It is to be noted that the charge carriers in p-doped layer 126have relatively low mobility compared to the charge carriers in then-doped semiconductor layer 134. As a result, placing silver layer 126(which is conductive) along the surface of p-doped layer 128 can enhancethe uniformity of charge injection from contact pad 138 into p-dopedlayer 128 and light-generating region 130. This can also reduce theelectrical resistance of device 100 and/or increase the injectionefficiency of device 100. Because of the relatively high charge carriermobility of the n-doped layer 134, electrons can spread relativelyquickly from n-side contact pad 136 throughout layers 132 and 134, sothat the current density within the light-generating region 130 issubstantially uniform across the region 130. It is also to be noted thatsilver layer 126 has relatively high thermal conductivity, allowinglayer 126 to act as a heat sink for LED 100 (to transfer heat verticallyfrom the multi-layer stack 122 to submount 120).

[0088] At least some of the light that is generated by region 130 isdirected toward silver layer 126. This light can be reflected by layer126 and emerge from LED 100 via surface 110, or can be reflected bylayer 126 and then absorbed within the semiconductor material in LED 100to produce an electron-hole pair that can combine in region 130, causingregion 130 to generate light. Similarly, at least some of the light thatis generated by region 130 is directed toward pad 136. The underside ofpad 136 is formed of a material (e.g., a Ti/Al/Ni/Au alloy) that canreflect at least some of the light generated by light-generating region130. Accordingly, the light that is directed to pad 136 can be reflectedby pad 136 and subsequently emerge from LED 100 via surface 110 (e.g.,by being reflected from silver layer 126), or the light that is directedto pad 136 can be reflected by pad 136 and then absorbed within thesemiconductor material in LED 100 to produce an electron-hole pair thatcan combine in region 130, causing region 130 to generate light (e.g.,with or without being reflected by silver layer 126).

[0089] As shown in FIGS. 1 and 2, surface 110 of LED 100 is not flat butconsists of a modified triangular pattern of openings 150. In general,various values can be selected for the depth of openings 150, thediameter of openings 150 and the spacing between nearest neighbors inopenings 150 can vary. Unless otherwise noted, for purposes of thefigures below showing the results of numerical calculations, openings150 have a depth 146 equal to about 280 nm, a non-zero diameter of about160 nm, a spacing between nearest neighbors or about 220 nm, and anindex of refraction equal to 1.0. The triangular pattern is detuned sothat the nearest neighbors in pattern 150 have a center-to-centerdistance with a value between (a−Δa) and (a+Δa), where “a” is thelattice constant for an ideal triangular pattern and “Δa” is a detuningparameter with dimensions of length and where the detuning can occur inrandom directions. To enhance light extraction from LED 100 (seediscussion below), detuning parameter, Δa, is generally at least aboutone percent (e.g., at least about two percent, at least about threepercent, at least about four percent, at least about five percent) ofideal lattice constant, a, and/or at most about 25% (e.g., at most about20%, at most about 15%, at most about 10%) of ideal lattice constant, a.In some embodiments, the nearest neighbor spacings vary substantiallyrandomly between (a−Δa) and (a+Δa), such that pattern 150 issubstantially randomly detuned.

[0090] For the modified triangular pattern of openings 150, it has beenfound that a non-zero detuning parameter enhances the extractionefficiency of an LED 100. For LED 100 described above, as the detuningparameter Δa increases from zero to about 0.15a, numerical modeling(described below) of the electromagnetic fields in the LED 100 has shownthat the extraction efficiency of the device increases from about 0.60to about 0.70, as shown in FIG. 3.

[0091] The extraction efficiency data shown in FIG. 3 are calculated byusing a three-dimensional finite-difference time-domain (FDTD) method toapproximate solutions to Maxwell's equations for the light within andoutside of LED 100. See, for example, K. S. Kunz and R. J. Luebbers, TheFinite-Difference Time-Domain Methods (CRC, Boca Raton, Fla., 1993); A.Taflove, Computational Electrodynamics: The Finite-DifferenceTime-Domain Method (Artech House, London, 1995), both of which arehereby incorporated by reference. To represent the optical behavior ofLED 100 with a particular pattern 150, input parameters in a FDTDcalculation include the center frequency and bandwidth of the lightemitted by the point dipole radiation sources in light-generating region130, the dimensions and dielectric properties of the layers withinmultilayer stack 122, and the diameters, depths, and nearest neighbordistances (NND) between openings in pattern 150.

[0092] In certain embodiments, extraction efficiency data for LED 100are calculated using an FDTD method as follows. The FDTD method is usedto solve the full-vector time-dependent Maxwell's equations:$\begin{matrix}{{{\overset{->}{\nabla}{\times \overset{->}{E}}} = {{- \mu}\quad \frac{\partial\overset{->}{H}}{\partial t}}},} & {{{\overset{->}{\nabla}{\times \overset{->}{H}}} = {{ɛ_{\infty}\frac{\partial\overset{->}{E}}{\partial t}} + \frac{\partial\overset{->}{P}}{\partial t}}},}\end{matrix}$

[0093] where the polarizability {right arrow over (P)}={right arrow over(P)}₁+{right arrow over (P)}₂+ . . . +{right arrow over (P)}_(m)captures the frequency-dependent response of the quantum welllight-generating region 130, the p-contact layer 126 and other layerswithin LED 100. The individual {right arrow over (P)}_(m) terms areempirically derived values of different contributions to the overallpolarizability of a material (e.g., the polarization response for boundelectron oscillations, the polarization response for free electronoscillations). In particular,${{\frac{^{2}{\overset{->}{P}}_{m}}{t^{2}} + {\gamma_{m}\frac{{\overset{->}{P}}_{m}}{t}} + {\omega_{m}^{2}{\overset{->}{P}}_{m}}} = {{ɛ(\omega)}\overset{->}{E}}},$

[0094] where the polarization corresponds to a dielectric constant${ɛ(\omega)} = {ɛ_{\infty} + {\sum\limits_{m}{\frac{s_{m}}{\omega_{m}^{2} - \omega^{2} - {\quad \gamma_{m}\omega}}.}}}$

[0095] For purposes of the numerical calculations, the only layers thatare considered are encapsulant 144, silver layer 126 and layers betweenencapsulant 144 and silver layer 126. This approximation is based on theassumption that encapsulant 144 and layer 126 are thick enough so thatsurrounding layers do not influence the optical performance of LED 100.The relevant structures within LED 100 that are assumed to have afrequency dependent dielectric constant are silver layer 126 andlight-generating region 130. The other relevant layers within LED 100are assumed to not have frequency dependent dielectric constants. It isto be noted that in embodiments in which LED 100 includes additionalmetal layers between encapsulant 144 and silver layer 126, each of theadditional metal layers will have a corresponding frequency dependentdielectric constant. It is also to be noted that silver layer 126 (andany other metal layer in LED 100) has a frequency dependent term forboth bound electrons and free electrons, whereas light-generating region130 has a frequency dependent term for bound electrons but does not havea frequency dependent term for free electrons. In certain embodiments,other terms can be included when modeling the frequency dependence ofthe dielectric constant. Such terms may include, for example,electron-phonon interactions, atomic polarizations, ionic polarizationsand/or molecular polarizations.

[0096] The emission of light from the quantum well region oflight-generating region 130 is modeled by incorporating a number ofrandomly-placed, constant-current dipole sources within thelight-generating region 130, each emitting short Gaussian pulses ofspectral width equal to that of the actual quantum well, each withrandom initial phase and start-time.

[0097] To cope with the pattern of openings 150 in surface 110 of theLED 100, a large supercell in the lateral direction is used, along withperiodic boundary conditions. This can assist in simulating relativelylarge (e.g., greater than 0.01 mm on edge) device sizes. The fullevolution equations are solved in time, long after all dipole sourceshave emitted their energy, until no energy remains in the system. Duringthe simulation, the total energy emitted, the energy flux extractedthrough top surface 110, and the energy absorbed by the quantum wellsand the n-doped layer is monitored. Through Fourier transforms both intime and space, frequency and angle resolved data of the extracted fluxare obtained, and therefore an angle- and frequency-resolved extractionefficiency can be calculated. By matching the total energy emitted withthe experimentally known luminescence of light-generating region 130,absolute angle-resolved extraction in lumens/per solid angle/per chiparea for given electrical input is obtained.

[0098] Without wishing to be bound by theory, it is believed that thedetuned pattern 150 can enhance the efficiency with which lightgenerated in region 130 emerges from LED 100 via surface 110 becauseopenings 150 create a dielectric function that varies spatially in layer134 according to pattern 150. It is believed that this alters thedensity of radiation modes (i.e., light modes that emerge from surface110) and guided modes (i.e., light modes that are confined withinmulti-layer stack 122) within LED 100, and that this alteration to thedensity of radiation modes and guided modes within LED 100 results insome light that would otherwise be emitted into guided modes in theabsence of pattern 150 being scattered (e.g., Bragg scattered) intomodes that can leak into radiation modes. In certain embodiments, it isbelieved that pattern 150 (e.g., the pattern discussed above, or one ofthe patterns discussed below) can eliminate all of the guided modeswithin LED 100.

[0099] It is believed that the effect of detuning of the lattice can beunderstood by considering Bragg scattering off of a crystal having pointscattering sites. For a perfect lattice arranged in lattice planesseparated by a distance d, monochromatic light of wavelength λ isscattered through an angle θ according to the Bragg condition, nλ=2d sinθ, where n is an integer that gives the order of the scattering.However, it is believed that for a light source having a spectralbandwidth Δλ/λ and emitting into a solid angle ΔΘ, the Bragg conditioncan be relaxed by detuning the spacing of between lattice sites by adetuning parameter Δa. It is believed that detuning the latticeincreases the scattering effectiveness and angular acceptance of thepattern over the spectral bandwidth and spatial emission profile of thesource.

[0100] While a modified triangular pattern 150 having a non-zerodetuning parameter Δa has been described that can enhance lightextraction from LED 100, other patterns can also be used to enhancelight extraction from LED 100. When determining whether a given patternenhances light extraction from LED 100 and/or what pattern of openingsmay be used to enhance light extraction from LED 100, physical insightmay first be used to approximate a basic pattern that can enhance lightextraction before conducting such numerical calculations.

[0101] The extraction efficiency of LED 100 can be further understood(e.g., in the weak scattering regime) by considering the Fouriertransform of the dielectric function that varies spatially according topattern 150. FIG. 4 depicts the Fourier transform for an idealtriangular lattice. Extraction of light into a particular direction within-plane wavevector k is related to the source emission S_(k′) into allthose modes with in-plane wavevector k′ (i.e. parallel to pattern 150)that are compatible to k by the addition or subtraction of a reciprocallattice vector G, i.e k=k′±G. The extraction efficiency is proportionalto the magnitude of the corresponding Fourier component (F_(k)) of thedielectric function ε_(G) given by $\begin{matrix}{{F_{\overset{->}{k}} = {c_{\overset{->}{k}}{\sum\limits_{\overset{->}{G}}{ɛ_{\overset{->}{G}}S_{\overset{->}{k} - \overset{->}{G}}}}}},} & {ɛ_{\overset{->}{G}} = {\int{{ɛ\left( \overset{->}{r} \right)}\quad ^{{- }\quad \overset{->}{G}\overset{->}{r}}{\overset{->}{r}}}}}\end{matrix}$

[0102] Since light propagating in the material generally satisfies theequation k²(in-plane)+k²(normal)=ε(ω/c)², the maximum G to be consideredis fixed by the frequency (ω) emitted by the light-generating region andthe dielectric constant of the light-generating region. As shown in FIG.4, this defines a ring in reciprocal space which is often called thelight line. The light line will be an annulus due to the finitebandwidth of the light-generating region but for sake of clarity weillustrate the light line of a monochromatic source. Similarly, lightpropagating within the encapsulant is bounded by a light line (the innercircle in FIG. 4). Therefore, the extraction efficiency is improved byincreasing F_(k) for all directions k that lie within the encapsulantlight-line which amounts to increasing the number of G points within theencapsulant light line and increasing the scattering strength ε_(G) forG points which lie within the material light line. This physical insightcan be used when selecting patterns that can improve extractionefficiency.

[0103] As an example, FIG. 5 shows the effect of increasing latticeconstant for an ideal triangular pattern. The data shown in FIG. 5 arecalculated using the parameters given for LED 100 shown in FIG. 1,except that the emitted light has a peak wavelength of 450 nm, and thedepth of the holes, the diameter of the holes, and the thickness of then-doped layer 134 scale with the nearest neighbor distance, a, as 1.27a,0.72a, and 1.27a+40 nm, respectively. Increasing the lattice constant,increases the density of G points within the light-line of theencapsulant. A clear trend in extraction efficiency with NND isobserved. It is believed that the maximum extraction efficiency occursfor NND approximately equal to the wavelength of light in vacuum. Thereason a maximum is achieved, is that as the NND becomes much largerthan the wavelength of light, the scattering effect is reduced becausethe material becomes more uniform.

[0104] As another example, FIG. 6 shows the effect of increasing holesize or filling factor. The filling factor for a triangular pattern isgiven by (2π/{square root}3)*(r/a)², where r is the radius of a hole.The data shown in FIG. 6 are calculated using the parameters given forthe LED 100 shown in FIG. 1, except that the diameter of the openings ischanged according the filling factor value given on the x-axis of thegraph. The extraction efficiency increases with filling factor as thescattering strengths (ε_(G)) increase. A maximum is observed for thisparticular system at a filling factor of ˜48%. In certain embodiments,LED 100 has a filling factor of at least about 10% (e.g., at least about15%, at least about 20%) and/or at most about 90% (e.g., at most about80%, at most about 70%, at most about 60%).

[0105] While a modified triangular pattern has been described in which adetuning parameter relates to positioning of openings in the patternfrom the positions in an ideal triangular lattice, a modified (detuned)triangular pattern may also be achieved by modifying the holes in anideal triangular pattern while keeping the centers at the positions foran ideal triangular pattern. FIG. 7 shows an embodiment of such apattern. The enhancement in light extraction, the methodology forconducting the corresponding numerical calculation, and the physicalexplanation of the enhanced light extraction for a light-emitting devicehaving the pattern shown in FIG. 7 is generally the same as describedabove. In some embodiments, a modified (detuned) pattern can haveopenings that are displaced from the ideal locations and openings at theideal locations but with varying diameters.

[0106] In other embodiments, enhanced light extraction from alight-emitting device can be achieved by using different types ofpatterns, including, for example, complex periodic patterns andnonperiodic patterns. As referred to herein, a complex periodic patternis a pattern that has more than one feature in each unit cell thatrepeats in a periodic fashion. Examples of complex periodic patternsinclude honeycomb patterns, honeycomb base patterns, (2×2) basepatterns, ring patterns, and Archimidean patterns. As discussed below,in some embodiments, a complex periodic pattern can have certainopenings with one diameter and other openings with a smaller diameter.As referred to herein, a nonperiodic pattern is a pattern that has notranslational symmetry over a unit cell that has a length that is atleast 50 times the peak wavelength of light generated by region 130.Examples of nonperiodic patterns include aperiodic patterns,quasicrystalline patterns, Robinson patterns, and Amman patterns.

[0107]FIG. 8 shows numerical calculations for LED 100 for two differentcomplex periodic patterns in which certain openings in the patterns havea particular diameter, and other openings in the patterns have smallerdiameters. The numerical calculations represented in FIG. 8 show thebehavior of the extraction efficiency (larger holes with a diameter of80 nm) as the diameter of the smaller holes (dR) is varied from zero nmto 95 nm. The data shown in FIG. 6 are calculated using the parametersgiven for the LED 100 shown in FIG. 1, except that the diameter of theopenings is changed according the filling factor value given on thex-axis of the graph. Without wishing to be bound by theory, multiplehole sizes allow scattering from multiple periodicities within thepattern, therefore increasing the angular acceptance and spectraleffectiveness of the pattern. The enhancement in light extraction, themethodology for conducting the corresponding numerical calculation, andthe physical explanation of the enhanced light extraction for alight-emitting device having the pattern shown in FIG. 8 is generallythe same as described above.

[0108]FIG. 9 shows numerical calculations for LED 100 having differentring patterns (complex periodic patterns). The number of holes in thefirst ring surrounding the central hole is different (six, eight or 10)for the different ring patterns. The data shown in FIG. 9 are calculatedusing the parameters given for the LED 100 shown in FIG. 1, except thatthe emitted light has a peak wavelength of 450 nm. The numericalcalculations represented in FIG. 9 show the extraction efficiency of LED100 as the number of ring patterns per unit cell that is repeated acrossa unit cell is varied from two to four. The enhancement in lightextraction, the methodology for conducting the corresponding numericalcalculation, and the physical explanation of the enhanced lightextraction for a light-emitting device having the pattern shown in FIG.9 is generally the same as described above.

[0109]FIG. 10 shows numerical calculations for LED 100 having anArchimidean pattern. The Archimedean pattern A7 consists of hexagonalunit cells 230 of 7 equally-spaced holes with a nearest neighbordistance of a. Within a unit cell 230, six holes are arranged in theshape of a regular hexagon and the seventh hole is located at the centerof the hexagon. The hexagonal unit cells 230 then fit together alongtheir edges with a center-to-center spacing between the unit cells ofa′=a*(1+{square root}3) to pattern the entire surface of the LED. Thisis known as an A7 tiling, because 7 holes make up the unit cell.Similarly, the Archimidean tiling A19 consists of 19 equally-spacedholes with a NND of a. The holes are arranged in the form of an innerhexagon of seven holes, and outer hexagon of 12 holes, and a centralhole within the inner hexagon. The hexagonal unit cells 230 then fittogether along their edges with a center-to-center spacing between theunit cells of a′=a*(3+{square root}3) to pattern the entire surface ofthe LED. The enhancement in light extraction, the methodology forconducting the corresponding numerical calculation, and the physicalexplanation of the enhanced light extraction for a light-emitting devicehaving the pattern shown in FIG. 10 is generally the same as describedabove. As shown in FIG. 10 the extraction efficiency for A7 and A19 isabout 77%. The data shown in FIG. 10 are calculated using the parametersgiven for the LED 100 shown in FIG. 1, except that the emitted light hasa peak wavelength of 450 and except that the NND is defined as thedistance between openings within an individual cell.

[0110]FIG. 11 shows numerical calculation data for LED 100 having aquasicrystalline pattern. Quasicrystalline patterns are described, forexample, in M. Senechal, Quasicrystals and Geometry (CambridgeUniversity Press, Cambridge, England 1996), which is hereby incorporatedby reference. The numerical calculations show the behavior of theextraction efficiency as the class of 8-fold based quasi-periodicstructure is varied. It is believed that quasicrystalline patternsexhibit high extraction efficiency due to high degree of in-planerotational symmetries allowed by such structures. The enhancement inlight extraction, the methodology for conducting the correspondingnumerical calculation, and the physical explanation of the enhancedlight extraction for a light-emitting device having the pattern shown inFIG. 11 is generally the same as described above. Results from FDTDcalculations shown in FIG. 11 indicate that the extraction efficiency ofquasicrystalline structures reaches about 82%. The data shown in FIG. 11are calculated using the parameters given for the LED 100 shown in FIG.1, except that the emitted light has a peak wavelength of 450 and exceptthat the NND is defined as the distance between openings within anindividual cell.

[0111] While certain examples of patterns have been described herein, itis believed that other patterns can also enhance the light extractionfrom LED 100 if the patterns satisfy the basic principles discussedabove. For example, it is believed that adding detuning toquasicrystalline or complex periodic structures can increase extractionefficiency.

[0112] In some embodiments, at least about 45% (e.g., at least about50%, at least about 55%, at least about 60%, at least about 70%, atleast about 80%, at least about 90%, at least about 95%) of the totalamount of light generated by light-generating region 130 that emergesfrom LED 100 emerges via surface 110.

[0113] In certain embodiments, the cross-sectional area of LED 100 canbe relatively large, while still exhibiting efficient light extractionfrom LED 100. For example, one or more edges of LED 100 can be at leastabout one millimeter (e.g., at least about 1.5 millimeters, at leastabout two millimeters, at least about 2.5 millimeters, at least aboutthree millimeters), and at least about 45% (e.g., at least about 50%, atleast about 55%, at least about 60%, at least about 70%, at least about80%, at least about 90%, at least about 95%) of the total amount oflight generated by light-generating region 130 that emerges from LED 100emerges via surface 110. This can allow for an LED to have a relativelylarge cross-section (e.g., at least about one millimeter by at leastabout one millimeter) while exhibiting good power conversion efficiency.

[0114] In some embodiments, the extraction efficiency of an LED havingthe design of LED 100 is substantially independent of the length of theedge of the LED. For example, the difference between the extractionefficiency of an LED having the design of LED 100 and one or more edgeshaving a length of about 0.25 millimeter and the extraction efficiencyof LED having the design of LED 100 and one or more edges having alength of one millimeter can vary by less than about 10% (e.g., lessthan about 8%, less than about 5%, less than about 3%). As referred toherein, the extraction efficiency of an LED is the ratio of the lightemitted by the LED to the amount of light generated by the device (whichcan be measured in terms of energy or photons). This can allow for anLED to have a relatively large cross-section (e.g., at least about onemillimeter by at least about one millimeter) while exhibiting good powerconversion efficiency.

[0115] In certain embodiments, the quantum efficiency of an LED havingthe design of LED 100 is substantially independent of the length of theedge of the LED. For example, the difference between the quantumefficiency of an LED having the design of LED 100 and one or more edgeshaving a length of about 0.25 millimeter and the quantum efficiency ofLED having the design of LED 100 and one or more edges having a lengthof one millimeter can vary by less than about 10% (e.g., less than about8%, less than about 5%, less than about 3%). As referred to herein, thequantum efficiency of an LED is the ratio of the number of photonsgenerated by the LED to the number of electron-hole recombinations thatoccur in the LED. This can allow for an LED to have a relatively largecross-section (e.g., at least about one millimeter by at least about onemillimeter) while exhibiting good performance.

[0116] In some embodiments, the wall plug efficiency of an LED havingthe design of LED 100 is substantially independent of the length of theedge of the LED. For example, the difference between the wall plugefficiency of an LED having the design of LED 100 and one or more edgeshaving a length of about 0.25 millimeter and the wall plug efficiency ofLED having the design of LED 100 and one or more edges having a lengthof one millimeter can vary by less than about 10% (e.g., less than about8%, less than about 5%, less than about 3%). As referred to herein, thewall plug efficiency of an LED is the product of the injectionefficiency of the LED (the ratio of the numbers of carriers injectedinto the device to the number of carriers that recombine in thelight-generating region of the device), the radiative efficiency of theLED (the ratio of electron-hole recombinations that result in aradiative event to the total number of electron-hole recombinations),and the extraction efficiency of the LED (the ratio of photons that areextracted from the LED to the total number of photons created). This canallow for an LED to have a relatively large cross-section (e.g., atleast about one millimeter by at least about one millimeter) whileexhibiting good performance.

[0117] In some embodiments, it may be desirable to manipulate theangular distribution of light that emerges from LED 100 via surface 110.To increase extraction efficiency into a given solid angle (e.g., into asolid angle around the direction normal to surface 110) we examine theFourier transform of the dielectric function that varies spatiallyaccording to pattern 150 (as described earlier). FIG. 12 shows theFourier transform construction for two ideal triangular lattices ofdifferent lattice constant. To increase the extraction efficiency, weseek to increase the number of G points within the encapsulant lightline and scattering strengths of G points (ε_(G)) within the materiallight line. This would imply increasing the NND so as to achieve theeffect depicted in FIG. 5. However, here we are concerned withincreasing the extraction efficiency into a solid angle centered aroundthe normal direction. Therefore, we would also like to limit theintroduction of higher order G points by reducing the radius of theencapsulant light line, such that the magnitude of G>(ω(n_(e)))/c. Wecan see that by decreasing the index of refraction of the encapsulant(the bare minimum of which is removing the encapsulant all together) weallow larger NND and therefore increase the number of G points withinthe material light line that are available to contribute to extractionin the normal direction (F_(k=0)) while simultaneously avoidingdiffraction into higher order (oblique angles) in the encapsulant. Theabove described trends are depicted in FIG. 13 which shows extractionefficiency into a solid angle (given by the collection half-angle in thediagram). The data shown in FIG. 13 are calculated using the parametersgiven for the LED 100 shown in FIG. 1, except that the emitted light hasa peak wavelength of 530 nm and a bandwidth of 34 nm, the index ofrefraction of the encapsulant was 1.0, the thickness of the p-dopedlayer was 160 nm, the light generating layer was 30 nm thick, the NND(a) for the three curves is shown on FIG. 13, and the depth, holediameter, and n-doped layer thickness scaled with a, as 1.27a, 0.72a,and 1.27a+40 nm, respectively. As the lattice constant is increased, theextraction efficiency at narrow angles increases as well as the overallextraction efficiency into all angles. However, for even larger latticeconstant, diffraction into higher order modes in the encapsulant limitsthe extraction efficiency at narrow angles even though the overallextraction efficiency increases into all angles. For a lattice constantof 460 nm, we calculate greater than 25% extraction efficiency into acollection half-angle of 30°. That is, about half of the extracted lightis collected within only about 13.4% of the upper hemisphere of solidangle demonstrating the collimation effect of the pattern. It isbelieved that any pattern that increases the number of G points withinthe material light line while limiting the number of G points within theencapsulant light line to only the G points at k=0 can improve theextraction efficiency into a solid angle centered around the normaldirection.

[0118] The approach is especially applicable for reducing the sourceetendue which is believed to often be proportional to n², where n is theindex of refraction of the surrounding material (e.g., the encapsulant).It is therefore believed that reducing the index of refraction of theencapsulating layer for LED 100 can lead to more collimated emission, alower source etendue, and therefore to a higher surface brightness (heredefined as the total lumens extracted into the etendue of the source).In some embodiments then, using an encapsulant of air will reduce thesource etendue while increasing extraction efficiency into a givencollection angle centered around the normal direction.

[0119] In certain embodiments, when light generated by region 130emerges from LED 100 via surface 110, the distribution of light is morecollimated than a lambertian distribution. For example, in someembodiments, when light generated by region 130 emerges from LED 100 viasurface 110, at least about 40% (e.g., at least about 50%, at leastabout 70%, at least about 90%) of the light emerging via the surface ofthe dielectric layer emerges within at most about 30° (e.g., at mostabout 25°, at most about 20°, at most about 15°) of an angle normal tosurface 110.

[0120] The ability to extract a relatively high percentage of light froma desired angle alone or coupled with a relatively high light extractioncan allow for a relatively high density of LEDs to be prepared on agiven wafer. For example, in some embodiments, a wafer has at leastabout five LEDs (e.g., at least about 25 LEDs, at least about 50 LEDs)per square centimeter.

[0121] In some embodiments, it may be desirable to modify thewavelength(s) of light that emerge(s) from a packaged LED 100 relativeto the wavelength(s) of light generated by light-generating region 130.For example, as shown in FIG. 14, an LED 300 having a layer containing aphosphor material 180 can be disposed on surface 110. The phosphormaterial can interact with light at the wavelength(s) generated byregion 130 to provide light at desired wavelength(s). In someembodiments, it may be desirable for the light that emerges frompackaged LED 100 to be substantially white light. In such embodiments,the phosphor material in layer 180 can be formed of, for example, a(Y,Gd)(Al,Ga)G:Ce³⁺ or “YAG” (yttrium, aluminum, garnet) phosphor. Whenpumped by blue light emitted from the light-generating region 130, thephosphor material in layer 180 can be activated and emit light (e.g.,isotropically) with a broad spectrum centered around yellow wavelengths.A viewer of the total light spectrum emerging from packaged LED 100 seesthe yellow phosphor broad emission spectrum and the blue InGaN narrowemission spectrum and typically mixes the two spectra to perceive white.

[0122] In certain embodiments, layer 180 can be substantially uniformlydisposed on surface 110. For example, the distance between the top 151of pattern 150 and the top 181 of layer 180 can vary by less than about20% (e.g., less than about 10%, less than about 5%, less than about 2%)across surface 110.

[0123] In general, the thickness of layer 180 is small compared to thecross-sectional dimensions of surface 130 of LED 100, which aretypically about one millimeter (mm) by one mm. Because layer 180 issubstantially uniformly deposited on surface 110, the phosphor materialin layer 180 can be substantially uniformly pumped by light emerging viasurface 110. The phosphor layer 180 is relatively thin compared to thedimensions of the surface 110 of the LED 100, such that light emitted bythe light-generating region 130 is converted into lower wavelength lightwithin the phosphor layer 180 approximately uniformly over the entiresurface 110 of LED 100. Thus, the relatively thin, uniform phosphorlayer 180 produces a uniform spectrum of white light emitted from theLED 100 as a function of position on surface 110.

[0124] In general, LED 100 can be fabricated as desired. Typically,fabrication of LED 100 involves various deposition, laser processing,lithography, and etching steps.

[0125] Referring to FIG. 15, a LED wafer 500 containing an LED layerstack of material deposited on a sapphire substrate is readily availableand can be purchased from a commercial vendor. On the sapphire substrate502 are disposed, consecutively, a buffer layer 504, an n-doped Si:GaNlayer 506, an AlGaN/GaN heterojunction or superlattice that provides acurrent spreading layer 508, an InGaN/GaN multi-quantum welllight-generating region 510, and a p-doped Mg:GaN layer 512. Thecommercially available LED wafer is about 2-3 inches in diameter andmultiple LED dice can be cut from the wafer to form individual devicesafter the wafer has been processed. Before dicing the wafer, a number ofwafer scale processing steps are used to position the p-doped layer 128on the same side of the light-generating region 130 as the mirror layer126.

[0126] Referring to FIG. 16, a relatively thin nickel layer 520 isdeposited (e.g., using electron-beam evaporation) on p-doped layer 512to form a p-type ohmic contact to p-doped layer 512. A silver layer 522is deposited (e.g., using electron-beam evaporation) on nickel layer520. A relatively thick nickel layer 524 is deposited on silver layer522 (e.g., using electron-beam evaporation). Layer 524 can act asdiffusion barrier to reduce the diffusion of contaminants into silverlayer 522. A gold layer 526 is deposited on nickel layer 524 (e.g.,using resistance evaporation). Wafer 500 is then annealed at atemperature between 400 and 600 degrees Celsius for between 30 and 300seconds in a nitrogen, oxygen, air, or forming gas to achieve an ohmiccontact.

[0127] Referring to FIG. 17, a submount wafer 600 is prepared bydepositing on a p-doped silicon wafer 602, consecutively (e.g., usingelectron-beam evaporation) an aluminum contact layer 604. A gold layer608 is deposited (e.g., using thermal evaporation) onto layer 604, and aAuSn bonding layer 610 is deposited (e.g., using thermal evaporation)onto layer 608. Submount wafer 600 is annealed at a temperature between350 and 500 degrees Celsius for between 30 and 300 seconds in anitrogen, oxygen, air, or forming gas to achieve an ohmic contact.

[0128] Wafer 500 and 600 are bonded together by bringing the layer 526into contact with layer 610 of the submount wafer 600 (e.g., using athermal-mechanical press) using pressures from 0 to 0.5 MPa andtemperatures ranging from 200-400 degrees Celsius. Layer 510 and layer610 form a eutectic bond. The combined wafer sandwich is cooled and thebonded sandwich is removed from the press.

[0129] After bonding, substrate 502 is removed from the combinedstructure by a laser liftoff process. Laser liftoff processes aredisclosed, for example, in U.S. Pat. Nos. 6,420,242 and 6,071,795, whichare hereby incorporated by reference. In some embodiments, a 248 nmlaser beam is shined through substrate 502 to locally heat n-dopedSi:GaN layer 506 near its interface with sapphire substrate 502,decomposing a sublayer of n-doped layer 506. The wafer sandwich is thenheated to above the melting point of gallium, at which point sapphiresubstrate 502 is removed from the sandwich by applying a lateral forceto it (e.g., using a cotton swab). The exposed GaN surface is thencleaned (e.g., using a hydrochloric acid bath) to remove liquid galliumfrom the surface. Often, when sapphire substrate 502 is removed from theGaN epitaxial layer stack, strain that was present in the stack (e.g.,due to the lattice mismatch between substrate 502 and the stack) isremoved from the stack. This can allow the stack to relax from a warpedor bowed shape it may have had when bonded to substrate 502, and toassume a relatively flat shape on the exposed surface of n-doped layer506. The coefficient of thermal expansion is considered when choosingthe submount to avoid cracking in the laser liftoff process. Inaddition, cracking can be reduced during laser-liftoff by substantiallyoverlapping fields in the step and repeat process.

[0130] Referring to FIG. 18, the exposed surface of n-doped Si:GaN layer506 is etched back (e.g., using a reactive ion etching process) toachieve a desired thickness for the layer to be used in the final device(FIG. 19). After etching, the surface of the etched GaN layer 506 has aroughened surface texture 700 due to the etching. Roughened surface 700can be planarized and thinned (e.g., using a chemical-mechanicalprocess) to achieve a final thickness for layer 506 and surfacesmoothness of less than about 5 nm root mean square (rms).Alternatively, roughened surface 700 can be maintained in order to aidin increasing the extraction efficiency of the device by introducing alocally non-planar interface to the device 100. The roughened surfaceincreases the probability, with respect to a microscopically smoothsurface, that a light ray that strikes surface 700 multiple times willeventually strike the surface at an angle that less than the criticalangle given by Snell's law and will be extracted through the surface700.

[0131] After etching, to prepare a dielectric function pattern in then-doped layer 506, first a planarization layer 702 of a material (e.g.,a polymer) is disposed (e.g., using spin-coating) onto n-doped GaN layer506 and a resist layer 704 is disposed (e.g., spin-coated) ontoplanarization layer 702. The pattern that forms the photonic lattice inthe LED is then created in n-doped layer 506 by a nanoimprintlithography and etching process. First, a mold that defines a portion ofthe desired pattern is pressed into the resist layer 704 and steppedacross the entire surface of the wafer in a portion-by-portion manner toprint the features of the pattern 150 and leaving regions for depositingn-contacts later on in the process flow. Preferably, the surface ofn-doped layer 506 is substantially flat during this portion of theprocess. X-ray lithography or deep ultraviolet lithography, for example,can also be used to create the pattern in resist layer 704. As analternative to depositing a resist on the wafer and creating a patternin the resist on the wafer, a predeposited etch mask can be laid down onthe surface of layer 506.

[0132] Patterned layer 704 is used as a mask to transfer the patterninto the planarization layer 702 (e.g., using a reactive-ion etchingprocess). Planarization layer is subsequently used as a mask to transferthe pattern into the n-doped layer 506. Following etching of GaN layer506, the planarization layer is removed (e.g., using an oxygen-basedreactive ion etch).

[0133] After the pattern has been transferred to n-doped layer 506, alayer of phosphor material can optionally be disposed (e.g.,spin-coated) onto the patterned surface of n-doped layer 506. In someembodiments, the phosphor can conformally coat the patterned surface(coat with substantially no voids present along the bottoms andsidewalls of the openings in the patterned surface). Alternatively, alayer of encapsulant material can be disposed on the surface ofpatterned n-doped layer 506 (e.g. by CVD, sputtering, suspension byliquid binder that is subsequently evaporated). In some embodiments, theencapsulant can contain one or more phosphor materials. In someembodiments, the phosphor can be compressed to achieve thicknessuniformity less that 20%, less than 15%, less than 10%, less than 5%, orless than 2% of the average thickness of the phosphor. In someembodiments, the phosphor-containing encapsulant can conformally coatthe patterned surface.

[0134] After the dielectric function pattern has been created in then-doped layer 506, individual LED dice can be cut from the wafer. Oncewafer processing and wafer testing is complete, individual LED dice areseparated and prepared for packaging and testing. A sidewall passivationstep and/or a pre-separation deep mesa etching step may be used toreduce potential damage to the electrical and/or optical properties ofthe patterned LED incurred during wafer cutting. The individual LEDs canbe any size up to the size of the wafer itself, but individual LEDs aretypically square or rectangular, with sides having a length betweenabout 0.5 mm to 5 mm. To create the dice, standard photolithography isused to define the location of contact pads on the wafer for energizingthe device, and ohmic contacts are evaporated (e.g. using electron beamevaporation) onto the desired locations.

[0135] If an LED die is packaged, the package should generally becapable of facilitating light collection while also providing mechanicaland environmental protection of the die. For example, a transparentcover can be packaged on the LED die to protect the patterned surface ofthe 506 when an encapsulant is not used. The cover slip is attached tosupports 142 using a glassy frit that is melted in a furnace. Theopposite ends of the supports are connected using a cap weld or an epoxyfor example. Supports are typically Ni-plated to facilitate welding toan Au plated surface of the package. It believed that the absence of anencapsulant layer allows higher tolerable power loads per unit area inthe patterned surface LED 100. Degradation of the encapsulant can be acommon failure mechanism for standard LEDs and is avoided not using anencapsulant layer.

[0136] Because the LEDs are cut from a large area flat wafer, theirlight output per area does not decrease with area. Also, because thecross section of an individual LEDs cut from a wafer is only slightlylarger than the light-emitting surface area of the LED, many individual,and separately addressable LEDs can be packed closely together in anarray. If one LED does not function (e.g., due to a large defect), thenit does not significant diminish the performance of the array becausethe individual devices are closely packed.

[0137] While certain embodiments have been described, other embodimentsare possible.

[0138] As an example, while certain thickness for a light-emittingdevice and associated layers are discussed above, other thicknesses arealso possible. In general, the light-emitting device can have anydesired thickness, and the individual layers within the light-emittingdevice can have any desired thickness. Typically, the thicknesses of thelayers within multi-layer stack 122 are chosen so as to increase thespatial overlap of the optical modes with light-generating region 130,to increase the output from light generated in region 130. Exemplarythicknesses for certain layers in a light-emitting device include thefollowing. In some embodiments, layer 134 can have a thickness of atleast about 100 nm (e.g., at least about 200 nm, at least about 300 nm,at least about 400 nm, at least about 500 nm) and/or at most about 10microns (e.g., at most about five microns, at most about three microns,at most about one micron). In certain embodiments, layer 128 has athickness of at least about 10 nm (e.g., at least about 25 nm, at leastabout 40 nm) and/or at most about one micron (e.g., at most about 500nm, at most about 100 nm). In some embodiments, layer 126 has athickness of at least about 10 nm (e.g., at least about 50 nm, at leastabout 100 nm) and/or at most about one micron (e.g., at most about 500nm, at most about 250 nm). In certain embodiments, light-generatingregion 130 has a thickness of at least about 10 nm (e.g., at least about25 nm, at least about 50 nm, at least about 100 nm) and/or at most about500 nm (e.g., at most about 250 nm, at most about 150 nm).

[0139] As an example, while a light-emitting diode has been described,other light-emitting devices having the above-described features (e.g.,patterns, processes) can be used. Such light-emitting devices includelasers and optical amplifiers.

[0140] As another example, while current spreading layer 132 has beendescribed as a separate layer from n-doped layer 134, in someembodiments, a current spreading layer can be integral with (e.g., aportion of) layer 134. In such embodiments, the current spreading layercan be a relatively highly n-doped portion of layer 134 or aheterojunction between (e.g. AlGaN/GaN) to form a 2 D electron gas.

[0141] As a further example, while certain semiconductor materials havebeen described, other semiconductor materials can also be used. Ingeneral, any semiconductor materials (e.g., III-V semiconductormaterials, organic semiconductor materials, silicon) can be used thatcan be used in a light-emitting device. Examples of otherlight-generating materials include InGaAsP, AlInGaN, AlGaAs, InGaAlP.Organic light-emitting materials include small molecules such asaluminum tris-8-hydroxyquinoline (Alq₃) and conjugated polymers such aspoly[2-methoxy-5-(2-ethylhexyloxy)-1,4-vinylenephenylene] or MEH-PPV.

[0142] As an additional example, while large area LEDs have beendescribed, the LEDs can also be small area LEDs (e.g., LEDs smaller thanthe standard about 300 microns on edge).

[0143] As another example, while a dielectric function that variesspatially according to a pattern has been described in which the patternis formed of holes, the pattern can also be formed in other ways. Forexample, a pattern can be formed continuous veins and/or discontinuousveins in the appropriate layer. Further, the pattern in varyingdielectric function can be achieved without using holes or veins. Forexample, materials having different dielectric functions can bepatterned in the appropriate layer. Combinations of such patterns canalso be used.

[0144] As a further example, while layer 126 has been described as beingformed of silver, other materials can also be used. In some embodiments,layer 126 is formed of a material that can reflect at least about 50% oflight generated by the light-generating region that impinges on thelayer of reflective material, the layer of reflective material beingbetween the support and the multi-layer stack of materials. Examples ofsuch materials include distributed Bragg reflector stacks and variousmetals and alloys, such as aluminum and aluminum-containing alloys.

[0145] As another example, support 120 can be formed of a variety ofmaterials. Examples of materials from which support 120 can be formedinclude copper, copper-tungsten, aluminum nitride, silicon carbide,beryllium-oxide, diamonds, TEC and aluminum.

[0146] As an additional example, while layer 126 has been described asbeing formed of a heat sink material, in some embodiments, alight-emitting device can include a separate layer (e.g., disposedbetween layer 126 and submount 120) that serves as a heat sink. In suchembodiments, layer 126 may or may not be formed of a material that canserve as a heat sink.

[0147] As a further example, while the varying pattern in dielectricfunction has been described as extending into n-doped layer 134 only(which can substantially reduce the likelihood of surface recombinationcarrier losses) in addition to making use of the entire light-generatingregion, in some embodiments, the varying pattern in dielectric functioncan extend beyond n-doped layer (e.g., into current spreading layer 132,light-generating region 130, and/or p-doped layer 128).

[0148] As another example, while embodiments have been described inwhich air can be disposed between surface 110 can cover slip 140, insome embodiments materials other than, or in an addition to, air can bedisposed between surface 110 and cover slip 140. Generally, suchmaterials have an index of refraction of at least about one and lessthan about 1.5 (e.g., less than about 1.4, less than about 1.3, lessthan about 1.2, less than about 1.1). Examples of such materials includenitrogen, air, or some higher thermal conductivity gas. In suchembodiments, surface 110 may or may not be patterned. For example,surface 110 may be non-patterned but may be roughened (i.e., havingrandomly distributed features of various sizes and shapes less thanλ/5).

[0149] In some embodiments, a light-emitting device can include a layerof a phosphor material coated on surface 110, cover layer 140 andsupports 142.

[0150] In certain embodiments, a light-emitting device can include acover layer 140 that has a phosphor material disposed therein. In suchembodiments, surface 110 may or may not be patterned.

[0151] In an alternative implementation, the light emitted by thelight-generating region 130 is UV (or violet, or blue) and the phosphorlayer 180 includes a mixture of a red phosphor material (e.g.,L₂O₂S:Eu³⁺), a green phosphor material (e.g, ZnS:Cu,Al,Mn), and bluephosphor material (e.g, (Sr,Ca,Ba,Mg)₁₀(PO₄)₆Cl:Eu²⁺).

[0152] Other embodiments are in the claims.

1. A light-emitting device, comprising: a multi-layer stack of materialsincluding a light-generating region, and a first layer supported by thelight-generating region, a surface of the first layer being configuredso that light generated by the light-generating region can emerge fromthe light-emitting device via the surface of the first layer; and amaterial in contact with the surface of the first layer, the materialhaving an index of refraction less than about 1.5, wherein the lightemitting device is packaged.
 2. The light-emitting device of claim 1,wherein the surface of the first layer has a dielectric function thatvaries spatially according to a pattern.
 3. The light-emitting device ofclaim 1, wherein the surface of the first layer has features with a sizeof less than about λ/5, where λ is a wavelength of light that can beemitted by the first layer.
 4. The light-emitting device of claim 1,wherein the light-emitting device is in the form of a packaged die. 5.The light-emitting device of claim 1, wherein the material comprises agas.
 6. The light-emitting device of claim 5, wherein the gas comprisesair.
 7. The light-emitting device of claim 5, wherein a pressure of thegas is less than about 100 Torr.
 8. The light-emitting device of claim1, wherein the material has an index of refraction of at least aboutone.
 9. The light-emitting device of claim 1, wherein the packagedlight-emitting device is free of an encapsulant material.
 10. Thelight-emitting device of claim 1, further comprising a cover, thematerial having an index of refraction of less than about 1.5 beingbetween the cover and the surface of the first layer.
 11. Thelight-emitting device of claim 10, wherein the cover comprises aphosphor material.
 12. The light-emitting device of claim 11, whereinthe cover is configured so that light generated by the light-generatingregion that emerges via the surface of the first layer can interact withthe phosphor material, and so that light that emerges via the surface ofthe first layer and interacts with the phosphor material emerges fromthe cover as substantially white light.
 13. The light-emitting device ofclaim 1, further comprising: a first sheet comprising a material that issubstantially transparent to light that emerges from the light-emittingdevice; and a second sheet comprising a phosphor material, the secondsheet being adjacent the first sheet, wherein the material having anindex of refraction of less than about 1.5 is between the first sheetand the surface of the first layer.
 14. The light-emitting device ofclaim 13, the first and second sheets being configured so that lightgenerated by the light-generating region that emerges via the surface ofthe first layer can interact with the phosphor material, and so thatlight that emerges via the surface of the first layer and interacts withthe phosphor material emerges from the second sheet as substantiallywhite light.
 15. The light-emitting device of claim 1, furthercomprising a support that supports the multi-layer stack of materials.16. The light-emitting device of claim 15, further comprising a layer ofreflective material that is capable of reflecting at least about 50% oflight generated by the light-generating region that impinges on thelayer of reflective material, the layer of reflective material beingbetween the support and the multi-layer stack of materials.
 17. Thelight-emitting device of claim 16, wherein the reflective material is aheat sink material.
 18. The light-emitting device of claim 17, whereinthe heat sink material is configured so that the heat sink material hasa vertical heat gradient during use of the light-emitting device. 19.The light-emitting device of claim 16, further comprising a heat sinkmaterial disposed adjacent the support.
 20. The light-emitting device ofclaim 19, wherein the heat sink material is configured so that the heatsink material has a vertical heat gradient during use of thelight-emitting device.
 21. The light-emitting device of claim 1, furtherincluding a current-spreading layer between the first layer and thelight-generating region.
 22. The light-emitting device of claim 1,further comprising electrical contacts configured to inject current intothe light-emitting device.
 23. The light-emitting device of claim 22,wherein the electrical contacts are configured to vertically injectelectrical current into the light-emitting device.
 24. Thelight-emitting device of claim 1, wherein the light-emitting device isselected from the group consisting of light-emitting diodes, lasers,optical amplifiers, and combinations thereof.
 25. The light-emittingdevice of claim 1, wherein the light-emitting device comprises a lightemitting diode.
 26. The light-emitting device of claim 1, wherein thelight-emitting device is selected from the group consisting of OLEDs,flat surface-emitting LEDs, HBLEDs, and combinations thereof.
 27. Thelight-emitting device of claim 1, wherein the surface of the first layerhas a dielectric function that varies spatially according to a patternwith an ideal lattice constant and a detuning parameter with a valuegreater than zero.
 28. The light-emitting device of claim 1, wherein thesurface of the first layer has a dielectric function that variesspatially according to a pattern, and the pattern does not extend intothe light-generating region.
 29. The light-emitting device of claim 1,wherein the surface of the first layer has a dielectric function thatvaries spatially according to a pattern, and the pattern does not extendbeyond the first layer.
 30. The light-emitting device of claim 1,wherein the surface of the first layer has a dielectric function thatvaries spatially according to a pattern, and the pattern extends beyondthe first layer.
 31. The light-emitting device of claim 1, furthercomprising a layer of reflective material that is capable of reflectingat least about 50% of light generated by the light-generating regionthat impinges on the layer of reflective material, wherein thelight-generating region is between the layer of reflective material andthe first layer.
 32. The light-emitting device of claim 1, furthercomprising a layer of reflective material that is capable of reflectingat least about 50% of light generated by the light-generating regionthat impinges on the layer of reflective material, wherein thelight-generating region is between the layer of reflective material andthe first layer.
 33. The light-emitting device of claim 1, wherein thesurface of the first layer has a dielectric function that variesspatially according to a nonperiodic pattern.
 34. The light-emittingdevice of claim 1, wherein the surface of the first layer has adielectric function that varies spatially according to a complexperiodic pattern.
 35. The light-emitting device of claim 2, wherein thesurface of the first layer has features with a size of less than aboutλ/5, where λ is a wavelength of light that can be emitted by the firstlayer.